During a power stroke of piston of an engine cylinder, a portion of the gases combusted within the cylinder may escape past a ring forming a seal around the piston base in a process known as blow-by. The escaped gases may accumulate in the crankcase, resulting in a buildup of pressure that may lead to degradation of oil stored in the crankcase to lubricate piston movement. The engine may include a crankcase ventilation system to vent gases out of the crankcase and into an engine intake manifold to provide continual evacuation of gases from inside the crankcase in order to reduce degradation of various engine components in the crankcase. The crankcase ventilation system may include a positive crankcase ventilation valve (PCV valve) for enabling one-way flow of crankcase gases from inside the crankcase to the intake manifold.
Crankcase ventilation systems may be intermittently diagnosed for PCV valve degradation. One example approach for PCV valve diagnostics is shown by Satou in US 2009/0211545. Therein, PCV valve degradation is determined based on air changes (e.g., changes to a throttle position) and fuel changes (e.g., fuel injection adjustments) required to maintain an idle speed as an opening of the PCV valve is adjusted. The opening of the PCV valve is, in turn, selected based on an air/fuel ratio of blow-by gas.
However, the inventors herein have recognized potential issues with such approaches. As one example, the blow-by based diagnostics approach may have significant noise issues due to various engine loads. These include, for example, engine friction, barometric pressure, AC compressor load, alternator load, etc. Consequently, computation intensive noise reduction algorithms may be required. In hybrid electric vehicles (HEV) and plug-in hybrid electric vehicles (PHEV), engine run time may be limited, thereby providing fewer opportunities for PCV valve diagnostics. Other sources of degradation such as in the cylinder valves may limit identification of a PCV valve degradation during a PCV system diagnostic routine.
In one approach to at least partially address these issues, a method for an engine crankcase ventilation system is provided. The method for an engine comprises: differentiating between degradation of a positive crankcase ventilation system (PCV) valve, a crankcase ventilation tube, and a cylinder valve based on a rate of pressure bleed-up in a PCV system during each of a cold-engine condition and a hot-engine condition. In this way, by carrying out PCV system diagnostics in the cold engine condition and the hot engine condition, PCV valve degradation and cylinder valve degradation may be identified and differentiated.
In one example, the positive crankcase ventilation system may include each of an isolation valve coupled to a junction of crankcase ventilation tube and fresh air intake passage and a PCV valve coupled to PCV line. By closing each of the isolation valve and the PCV valve, the PCV system may be isolated from the air intake system. After an engine temperature reduces following an engine shut-down, a cold-engine PCV diagnostic routine may be initiated. The diagnostic routine may include closing the isolation valve and spinning the engine unfueled to generate an intake system vacuum. Once a desired intake system vacuum level is reached, a variable displacement engine (VDE) mechanism may be used to deactivate each of the deactivatable cylinders and the cylinder valves (intake valves and exhaust valves) of the deactivatable cylinders may be closed. Further, the engine may be rotated to stop at a desired position where the cylinder valves of the non-deactivatable cylinders are closed, thereby closing all cylinder valves. The PCV system may be evacuated via the PCV valve and once the vacuum is transferred to the PCV system, the PCV valve may be passively or actively closed. The vacuum decay in the PCV system may be monitored via a pressure sensor coupled to the crankcase ventilation tube. If it is determined that the rate of vacuum decay is lower than a threshold, it may be indicated that the PCV valve and the cylinder valves are not degraded. However, if it is determined that the rate of vacuum decay is higher than a threshold, immediately after a subsequent engine shut-down, a hot-engine PCV diagnostic routine may be initiated. If during the hot-engine diagnostic routine, the rate of vacuum decay in the PCV system is higher than a threshold, it may be indicated that the PCV valve is degraded. However, if during the hot-engine diagnostic routine, the rate of vacuum decay in the PCV system is lower than a threshold, it may be indicated that the PCV valve is not degraded but the cylinder valves may be degraded. Appropriate mitigating actions may be taken in response to detection of PCV valve/cylinder valves degradation.
In this way, by sealing the PCV system and monitoring vacuum decay in the PCV system during both cold-engine condition and hot-engine condition, PCV valve degradation and engine cylinder valve degradation may be identified and appropriate mitigating steps may be undertaken during subsequent engine cycles. By introducing the PCV isolation valve, it is possible to seal the PCV system when desired. The technical effect of carrying out the PCV system diagnostics during a vehicle key-off condition is that the diagnostics may be periodically carried out in HEV and PHEV vehicles where engine run time may be limited. Also, by carrying out the diagnostics during the vehicle key-off condition, change in engine noise due to the diagnostic routine may not be encountered by the operator. Overall, by regularly monitoring the health of the PCV system, desired engine emissions quality and fuel efficiency may be maintained.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.